Crude aortic preparations contain an unidentified protein which inhibits cholesteryl esterase. We will investigate its properties as well as its presence and activity in resistant and susceptible animals species. Our previous work has shown that the ratio of aortic cholesteryl ester synthetase/cholesteryl ester hydrolase (S/H) is higer in species susceptible to atherosclerosis than in resistant species. We propose to investigate S/H ratios in male and female rabbits and rats. The study will entail use of aortas from intact and castrated animals. We will investigate effects of atherogenic diets on levels of N-acetyl-Beta-D-hexosaminidase and its isozymes in rabbit serum.